Pedal drive system

ABSTRACT

A pedal drive system, in particular for an electric vehicle or a training apparatus, and for generating electrical power from muscle power of a user with at least one pedal and an electric generator, connected mechanically with said at least one pedal, is provided. To improve the haptic feel and feedback at the pedal, a control unit is provided for controlling a feedback torque, applied at said pedal, wherein the control unit comprises a haptic renderer, configured for control of said feedback torque based on at least one user-defined pedal reference trajectory.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation-in-part application ofU.S. patent application Ser. No. 16/072,452, filed as PCT/EP2016/071602on Sep. 13, 2016. PCT/EP2016/071602 claims priority benefit of EP16152850.0, filed on Jan. 26, 2016. The contents of the aforementionedapplications and of publication WO 00/059773 A2 are incorporated hereinby reference for all purposes to the extent that such subject matter isnot inconsistent herewith or limiting hereof.

TECHNICAL FIELD

The present invention relates to the field of electric transportation,in particular to muscle-operated vehicles, and to drive systems forelectric vehicles.

BACKGROUND

In the field of transportation, the continued development of batterytechnology enabled intensified use of electrically powered vehicles. Itis estimated that the use of electrically powered vehicles, alsoreferred to as “electric vehicles”, will continue to rise in the nearfuture. Besides vehicles that are entirely operated using electricpower, hybrid vehicles are available using various drivetrain setups,such as parallel- and series-type hybrid vehicles. For example, hybridvehicles are commercially available, which are in part operated bymuscle power of an operator, and which also comprise an electric motor,e.g., for support of the operator, to minimize fatigue and to extend therange. Such drive concepts are in particular used in bicycles,tricycles, quadracycles, boats, airplanes or helicopters, i.e.,virtually in any type of vehicle.

In the recent past, series-type hybrid drives have been made available,where an operator provides input muscle power by using one or twofoot-pedals, levers, or handles. The provided input muscle power isconverted into electric energy using a generator, which is mechanicallycoupled to the respective pedal, lever, or handle. The electric energyis then fed to an electric motor to drive the vehicle, e.g., togetherwith electric energy from a battery in case some support, also known as“power assist”, is required. Accordingly, vehicles using this setup arealso referred to as having an “electric transmission”, since there is noconnection between pedal and wheel that could convey mechanicalpropulsive power. These vehicles are similar to the common “Pedelecs”,but the mechanical setup of such vehicles is much simpler and thuscheaper than the typical setup of a Pedelec, in particular since nochain, belt, or transmission shaft and no elaborate mechanical orhydraulical gear shift mechanism is necessary. In addition, hybridvehicles with an electric transmission can be configured in a flexibleway, e.g., to match the use of the respective operator.

A particular challenge with series-type, muscle-operated hybrid electricvehicles, however, is given in that an operator typically expects themechanical interaction, i.e., the “feel” or “feedback” of the drivesystem to be similar to that of a known corresponding vehicle having amechanical drivetrain. For example, in a case of a hybrid electricbicycle having pedals, an operator typically expects the pedals torespond like the pedals of a common “mechanical” bicycle, including theusual resistance torque of the pedal due to the inertia of the bicycleand its chain/wheel drive.

In a series-type hybrid electric vehicle, the mass of the pedals, thegenerator coupled to them and an optional transmission in betweenusually is negligible, e.g. in comparison to the total mass of thevehicle and the operator. Therefore, this mass does not give rise to anysignificant resistance torque. Further, some resistance torque isgenerated by “dissipative” or “damping” effects such as mechanicalfriction, eddy currents and hysteresis losses. The order of magnitude ofthe torque due to these effects can be e.g. 1-3 Nm, which is rather low.Also, the operator may experience an electrical resistance torque due tothe power generation in the generator. However, this torque, which, inmost electrical machines, is proportional to the output current of thegenerator, can also be relatively low, depending on the type ofgenerator and how it is operated. This leads to an unexpected “feel” ofthe drive system during use. The unexpected feel or behavior of suchvehicle may in turn be conceived by an operator as not particularlyergonomic. In addition, in the case of a foot-operated series-typeelectric bicycle, a lack of enough pedal resistance torque can possiblylead to dangerous situations. For example, upon starting to pedal, alack of pedal resistance torque may cause the operator to lose balanceon the vehicle or even slide off the pedal, since the behavior is not asit would be expected from a common bicycle having a traditional bicycledrive train.

In the prior art, the problem of an unexpected behavior of series-typehybrid electric vehicles was addressed, e.g., in WO 00/059773 A2 of thepresent inventor. The latter document in particular addresses thesituation upon starting to pedal and improves the behaviorsignificantly. US 2009/0095552 A1 describes a further approach toprovide a largely “natural” behavior of a series-type hybrid vehicle,comparable to a mechanically driven vehicle. Here, the speed of thepedal crank is related to the travel velocity in a way that iscomprehensible to a user of the vehicle. The system of US 2009/0095552A1 comprises a braking unit, which opposes the rotation of the pedalcrank. The braking unit may, e.g., comprise a flywheel mass. The pedalcrank of this reference is not primarily used for generating energy topropel the vehicle, but rather for controlling the travel velocity ofthe vehicle.

Certainly, carrying along a flywheel mass on an hybrid electric vehicleleads to a reduced efficiency due to unnecessary friction and increasedweight. But even without using a flywheel mass, the direct coupling ofthe pedal crank with the vehicle speed according to the prior art may bedisadvantageous, since due to the characteristic pedaling of a human,inevitable variations in the provided pedaling speed causes variationsin the vehicle speed, which in turn may result in poor vehicle handling,such as in particular reduced traction control on hard and slicksurfaces, e.g., during inclement weather conditions.

Accordingly, a pedal drive system is needed that provides an improvedhaptic feel and feedback to a user/operator, while avoiding one or moredisadvantages of the prior art.

SUMMARY

The following summary of the present invention is provided to facilitatean understanding of some of the innovative features unique to thepresent invention and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

According to one aspect of the present invention, a pedal drive systemfor generating electrical power from muscle power of a user is providedwith at least one pedal, an electric generator, connected mechanicallywith said at least one pedal, and a control unit for controlling afeedback torque, applied at said pedal. The control unit comprises ahaptic renderer, configured for control of said feedback torque based onat least one pedal reference trajectory. For sake of brevity, the useris in the following referred to as “he”. This, however, is intended toinclude female and male users, i.e., “she” and “he”.

The basic idea of the present invention is to provide a pedal drivesystem that allows to provide a controllable feedback torque to a user,which feedback torque is controlled by a control unit of the pedal drivesystem itself. In the context of electric vehicles, the presentinvention thus allows to decouple the control of the pedal drive fromthe control of the wheel drive. Accordingly, it is possible on one handto control the torque/feedback torque at the pedal as desired, whilesimultaneously it is also possible to control the wheel drive asdesired, i.e., according to the respective driving conditions.

The invention in the context of electric vehicles thus allows both,improved haptic feel and feedback at the pedal, as well as improvedvehicle handling. Certainly, the thus autonomous/independent pedal drivesystem can also be used outside of the field of electric land, water orair vehicles, such as in stationary exercise bikes, training apparatus,or other exercise or therapy devices.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 shows a schematic representation of components of an electricvehicle comprising an inventive pedal drive system and an inventiveelectric drive system;

FIG. 2 is a flow diagram showing the adaption of a feedback torque;

FIG. 3 is a flow diagram showing the adaption of a reference trajectory;

FIG. 4 is a diagram illustrating the evolution of an input torque and anangular velocity over crank angle;

FIG. 5 is a diagram showing the development of an input torque and theadaptation of a reference trajectory;

FIG. 6 is a diagram illustrating the time evolution of a cadence afterstarting operation of the vehicle;

FIG. 7 is a diagram illustrating the dependency of an average inputtorque as a function of an average cadence;

FIG. 8 is a diagram illustrating a reference plane for a maximumacceleration value of an inventive electric drive system;

FIG. 9 is a diagram illustrating the power generation allocated to theuser of an electric bicycle as a function of the battery current;

FIG. 10 shows a schematic representation of components of an electricvehicle 101 according to another embodiment; and

FIG. 11 is a flow diagram of the operation of control unit 30 of FIG. 10.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Technical features described in this application can be used toconstruct various embodiments of pedal drive systems, electric vehicles,training apparatus, electric drive systems, and methods for operating apedal drive system according to the preceding and following description.Some embodiments of the invention are discussed so as to enable oneskilled in the art to make and use the invention.

In the following explanation of the present invention according to theembodiments described, the terms “connected to” or “connected with” areused to indicate a connection between at least two components, elementsor modules. Such connection may be direct or indirect, i.e., overintermediate components, elements or modules.

In a first exemplary aspect, a pedal drive system for generatingelectrical power from muscle power of a user is provided with at leastone pedal, an electric generator, connected mechanically with said atleast one pedal, and a control unit for controlling a feedback torque,applied at said pedal. The control unit comprises a haptic renderer,configured for control of said feedback torque based on at least onepedal reference trajectory.

The pedal drive system according to the present aspect allows togenerate electrical energy from muscle power and correspondinglycomprises a pedal and an electric generator, wherein the electricgenerator is connected mechanically with said at least one pedal. In thepresent context, the term “connected mechanically” is understood tocomprise all suitable setups allowing to transfer a force from the pedalto the generator and vice versa. The connection may be direct orindirect over intermediate components, such as over a gear mechanism. Itis noted that the term “mechanical” in this context comprises setups,which are not strictly mechanical, but e.g. pneumatic or hydraulic.

Although in most embodiments, the at least one pedal may be provided toallow a rotational movement and thus to provide an input torque,provided by the user, it is noted that such may not necessarily be thecase. For example, in an alternative embodiment, the pedal may beprovided for the exertion of muscle power in a linear movement, whichthen consequently is converted into electric energy by a suitable lineargenerator or a mechanism converting a mostly linear movement into arotational movement if the generator is of a rotational type. In case ofa linear movement, certainly, the user would provide an input forceinstead of an input torque and the control unit would provide a feedbackforce instead of a feedback torque. However, the operation in this casecorresponds to the discussion below. For sake of simplicity, thefollowing description refers explicitly to the rotational quantitiesonly, i.e., torque, angular velocity etc. However, it is to beunderstood that this includes the corresponding linear quantities, i.e.,force instead of torque, linear velocity instead of angular velocity,etc.

Accordingly, the at least one pedal may for example be a foot pedal inone embodiment or a hand operated lever in another embodiment. In afurther embodiment, the pedal drive system is configured for bipedaloperation, comprising at least two pedals with associated cranks thatare provided in a typical bicycle pedal setup, i.e., for rotation arounda common axis of rotation, which e.g., may be a bottom bracket axle.

As discussed in the preceding, the pedal drive system further comprisesa control unit, which is configured to control a feedback torque,applied at the pedal. To this respect, the control unit is configuredfor active control. In the context of the present invention, the termfeedback torque comprises both a counter torque and a supporting, i.e.,assistive, torque. A counter torque is understood as a torque applied ina direction opposite to the input torque of the user. The counter torqueprovides a certain resistance to the user. A supporting torque isprovided in the direction of the input torque of the user, i.e., tosupport the pedaling effort of the user. It should be noted that asupporting torque as well as a counter torque can be provided byoperating the electric generator as a motor, i.e., in a “motor” mode. Acounter torque may also be provided by operating the electric generatorin a “normal” or “generator” mode, i.e., so that it generates electricenergy. The feedback torque accordingly provides a defined “hapticfeedback” to the user, which in one embodiment may provide the user witha feel similar to that of a known mechanical bicycle. Such“bicycle-similar” feel is understood to comprise a temporally andspatially well defined resistance at the pedal. The feedback torque in afurther embodiment is an electrically generated feedback torque, i.e.,provided by applying an electric current to the generator (in the“motor” mode) or by using the generator to deliver a current (in the“generator” mode) e.g. to an electrical load. The term “haptic” in thecontext of this explanation refers to a perception by making physicalcontact with the at least one pedal. To this extent this term refers tostrictly haptic perception as well as tactile and proprioceptiveperception.

Certainly, the pedal drive system described herein also allows toprovide a haptic feedback that differs from that of a mechanicalbicycle. For example, and in one embodiment, the pedal drive system maybe programmed with custom settings of a user, e.g., a predefinedoperating point, defined by a preferred cadence (“cadence” here and inthe following referring to the number of motion cycles—usuallyrotations—of the at least one pedal per time unit, which may also bereferred to as the pedal frequency), or a preferred gradient in terms ofthe change of the pedaling torque with the cadence (Nm/rpm) under load.In a further embodiment, the pedal drive system may be configured tosupport the user with a brief supporting torque, e.g. every time when apedal is at the top dead center during the pedal rotation. In anotherexemplary embodiment, the pedal drive system may be adapted forrehabilitation training applications with the respective requirements ofthe application. In such case, the user may be supported with asupporting torque for a larger part of the pedal rotation, e.g. in orderto compensate for a disablement of one leg of the user. Also, if a userhas limited control of the movement of at least one leg, it may benecessary to smoothen the movement of the at least one pedal by applyingan appropriate supporting or counter torque during the entire pedalrotation. Also, the haptic feedback may contain high frequencycomponents to signal something to the user, e.g. a warning of amalfunction of the vehicle or the drive system, or that personal limitslike maximum pedaling power or heart rate are exceeded. To signalsomething, high frequency components may be superimposed onto thereference trajectory, which would result in a “vibration alert” feeling.

The feedback torque can be applied during operation of the system,wherein the term “during operation” is understood broadly and means anystate of the system being powered, and is not limited to a state ofpedaling forward (or backward) of the user. For example, the controlunit may in one embodiment be configured to apply a holding or clampingtorque to the pedal before and/or after the pedaling of the user, whichin this context is also considered to be “during operation” of the pedaldrive system. The same applies for an embodiment in which the controlunit is configured to apply a supporting torque that assists the user inmoving the pedal backwards e.g. to an optimum starting position.

The control unit comprises at least a haptic renderer, as discussed inthe preceding. The haptic renderer is configured for control of thefeedback torque based on at least one predefined pedal referencetrajectory.

The pedal reference trajectory in one embodiment defines pedal cadenceand/or pedal acceleration over the pedal position/angle for at least apart of a pedal revolution. Of course, instead of pedal cadence, whichcorresponds to frequency, a pedal angular velocity may be used, whichonly differs by a constant factor of π/30 (with the angular velocitybeing measured in rad/s and the cadence being measured in 1/min).Instead of pedal position, it is alternatively or additionally inaccording embodiments possible that the pedal reference trajectory isdefined over time, which corresponds to a defined pedal position, oncethe system is initialized with a given set point. If given as a functionof time, the pedal trajectory may in general define the pedal angularposition and/or any of its time derivatives (angular velocity, angularacceleration, etc.). Any of the derivatives may also be defined as afunction of the pedal position. In further embodiments, the pedalreference trajectory provides a defined pedal cadence and/oracceleration behavior for a fraction of a revolution, for one revolutionor for multiple pedal revolutions. It should be noted that the angularposition can be calculated from its derivatives (apart from integrationconstants, which may be obtained by calibration or the like) and viceversa. To this respect, it is also possible that the trajectory isstored as information on one parameter, e.g. angular position, but isused as information on another parameter, e.g. cadence. In this case,the control unit is configured for a corresponding conversion.

The haptic renderer controls the feedback torque to obtain the desiredcourse of pedal cadence or acceleration according to the pedal referencetrajectory. The according control of the haptic renderer is based on thepresent inventor's recognition that with a human user, pedal cadence andacceleration can be controlled by the feedback torque provided to theuser, i.e., the pedaling resistance or support the user feels due to thegenerator working in “normal” mode or “motor” mode. The correspondingcontrol is somewhat similar to a force/torque control in the field ofrobotics or gaming.

In this concept, the reference trajectory to some extent may “simulate”or “reproduce” the inertia of a mechanical bicycle (i.e., a bicycle witha mechanical drivetrain). In such a mechanical bicycle, the inertia isfelt by a user at the pedals in that he cannot change the motion of thepedals abruptly and arbitrarily. The pedals rather appear to have an“increased” inertia which results from the mechanical coupling of thepedal(s) to a driven wheel, which in turn is coupled to the bicycle andthe user. Since the motion state of the bicycle cannot change abruptly,neither can the motion state of the pedals. I.e., at least for some timeinterval, the motion of the pedals is predetermined or limited. Thisbehavior of a mechanical bicycle can be simulated in the presentinvention by the predefined reference trajectory. However, the referencetrajectory does not necessarily have to represent (at least not exactly)a trajectory found in a mechanical bicycle, as discussed in thepreceding.

It should be noted that while the haptic renderer may provide asupporting torque as well as a counter torque, in some embodiments thesupporting torque may be limited. For instance, the supporting torquemay be limited to compensate a torque generated by frictional forces.Without any limitation like this, a supporting torque could pull thepedal and a user's foot (or hand, respectively) placed on the pedalalong a predefined reference trajectory, which could be unexpected anduncomfortable to the user. From his experience with mechanical bicycles,a user is used to a freewheel, which allows him to stop the motion ofthe pedals while the bicycle keeps moving on. To provide a similarfeeling to the user, the haptic renderer in an embodiment is adapted toprovide an “electronic freewheel” by limiting a supporting torque.However, in contrast to a freewheel in a mechanical bicycle, in anembodiment, a counter torque is always present when the user reduces thecadence. In a mechanical bicycle, reducing the cadence leads todecoupling the pedal from the driven wheel by the freewheel mechanism.In the present drive system, however, a counter torque which supportsthe reduction of the cadence may still be present. This has twoadvantages. On the one hand, the user still feels some resistance in thepedal, which may help to stabilize him. On the other hand, if thecounter torque is generated by the generator, kinetic energy from theuser's legs (or arms, respectively) can be converted into electricenergy, i.e., it can be recuperated. While in a mechanical bicycle, thepedal may only be either completely coupled to or completely decoupledfrom the driven wheel, the counter torque in a hybrid electric vehiclemay correspond to an “intermediate” coupling state.

The control unit may in a further embodiment comprise an inertiamodeler, configured to iteratively adapt the at least one pedalreference trajectory, which adapted pedal reference trajectory isprovided to the haptic renderer for control of said feedback torque.Micro-controllers available today allow fast, even massive computing andhence iterative operation of the inertia modeler. In particular,differences between an expected pedaling behavior according to thedesired pedal reference trajectory and the actual (current or past)pedaling behavior may be determined by the inertia modeler, which inturn adapts the reference trajectory based on the differences. Suchdifferences may indicate that the user is trying to accelerate ordecelerate by changing the applied input torque. However, the adaptionmay depend on other parameters, e.g. time or cadence, and does notnecessarily have to depend on variations of the actual pedalingbehavior. In particular, it may not depend on the state of operation ofany vehicle drive wheel(s).

Normally, the adaption of the pedal reference trajectory is carried outat predefined intervals, i.e., after a predetermined amount of time or,alternatively, after a predefined angular movement of the pedal. Thetime intervals do not have to be constant. Rather, the length of thetime intervals could depend e.g. on the present cadence or the presentvelocity of a vehicle driven by the drive system, its acceleration orwhether a computing device implementing the inertial modeler istemporarily doing other calculations. Also, the term “predetermined”does not imply that all intervals have to be predetermined when the userstarts operation of the drive system. In one simple mode of carrying outthe invention according to one embodiment, however, all intervals havethe same constant length, which is predetermined before operationbegins.

A correspondingly adapted pedal reference trajectory is provided to thehaptic renderer for control of the feedback torque. In general, theadapted reference trajectory will lead to a different feedback torque.E.g. if the user applies the same input torque, a different referencetrajectory may lead to a different feedback torque.

The control unit may be of any suitable type and in general may comprisea micro controller or micro processor, having a suitable programming toprovide the functionality of the described haptic renderer and—ifapplicable—the inertia modeler. The control unit may also be referred toas an “adapter” or an “abstraction layer”. This intermediate layerallows to physically decouple human and machine, but allows to displayan ergonomical pedaling behavior at the pedals and to realize adynamical but safe drive at the driving wheels (if such driving wheelsare present). In particular, field programmable gate arrays (FPGAs) maybe used in view of their fast current control and hence very fast torquecontrol.

In one embodiment, the haptic renderer is configured for impedancecontrol of said feedback torque so that movement of the pedal is adaptedto the pedal reference trajectory. As already indicated above, the atleast one pedal may be “guided” along the reference trajectory. As isknown from literature (e.g. from Fregly B J, Zajac F E, Dairaghi C A.Bicycle drive system dynamics: theory and experimental validation. JBiomech Eng. 2000 August; 122(4):446-52), the angular acceleration ofthe pedal crank of a mechanical bicycle can be calculated according tothe following equation:I _(eff) {umlaut over (θ)}=T _(c) −T _(eff)  (Eq. 1)

Where I_(eff) is the effective inertia about the crank axis, θ is thecrank angle, T_(c) is the crank torque generated by the user (i.e. theinput torque) and T_(eff) is the effective resistance torque. In thecase of (chainless) human-electric hybrid vehicles with electronictransmission, the effective resistance torque is caused by frictionalforces (in the bearings and in the transmission between the at least onepedal and the generator), by damping effects in the generator (such aseddy currents and hysteresis losses) and by the feedback torque (ingenerator or motor mode). Frictional forces can be known frommeasurements or calculations and are usually more or less constant.Losses in the generator typically depend on generator speed. Ohmiclosses are proportional to the square of the currents occurring in motoror generator mode. Thus, with the effective inertia known (which maye.g. be set or calculated) and the crank torque being known from direct(e.g. by force or torque measurement on pedals and/or gear components)or indirect measurement (e.g. by measuring a generator current which islargely proportional to the torque), it is possible to determine afeedback torque for a desired cadence, angular acceleration or otherquantity representing a reference trajectory.

In a further embodiment, the haptic renderer analyses the differencebetween a measured parameter, like angular position or angular velocity,and the corresponding “expected” parameter according to the referencetrajectory. A counter torque or supporting torque may be proportional tothe difference. It is also possible to combine several differences, e.g.of the angular position, the angular velocity and the sum (or integral)over several angular positions. While in this embodiment, the hapticrenderer is configured for impedance control of the feedback torque, itis alternatively conceivable that admittance control is used.

The term “adapted” does not imply that the movement of the pedal has tofollow the reference trajectory exactly. More generally, this means thatthe haptic renderer controls the feedback torque so that the movementeither follows the reference trajectory or is guided towards it. Interms of control theory, the reference trajectory can be regarded as thesetpoint or nominal value. As mentioned above, if the determinedfeedback torque is a supporting torque, its magnitude may be limited inorder to provide an electronic freewheel. Other limitations to thefeedback torque are possible, e.g. in order to prevent overload ofmechanical components.

According to another embodiment, the inertia modeler is configured toadapt the reference trajectory based on at least one trajectoryparameter. As mentioned above, the trajectory may be adapted accordingto the time that has passed since the beginning of its operation or thetime since the user has started pedaling. In this case, the time is usedas a trajectory parameter. Also, the current (average) cadence or thevelocity (speed) of a vehicle driven by the pedal drive system may be atrajectory parameter. These parameters may for instance have aninfluence on the variation of the angular velocity about a mean value.In order to reproduce the behavior of a mechanical bicycle, where theangular velocity of the pedals becomes more and more constant withincreasing velocity (mostly due to the increasing gear ratio and henceincreasing effective inertia), the amplitude of oscillation of theangular velocity in the reference trajectory may be reduced withincreasing velocity. This oscillation about a mean value may also bereferred to as a “ripple”. Other trajectory parameters may pertain tothe current status of the user, like his heart rate or blood sugarlevel, or the current charge level of an energy storage device, such ase.g. a rechargeable battery.

Furthermore, it is possible that a user sets one or several parametersof the reference trajectory using a control device or interface device,which may be an onboard device of a vehicle that is powered by the drivesystem like a traditional digital tachometer or a mobile device like asmartphone, a PDA, a tablet or the like. For instance, the user may seta preferred cadence or the slope of a function representing thedependence of an average feedback torque on the (average) cadence orother parameters made available to the controller.

According to one embodiment, the inertia modeler is configured to:

-   -   determine a past torque course for a predefined sampling time,    -   determine a reference torque course, corresponding to the        reference trajectory, for said predefined sampling time using a        vehicle model,    -   conduct a comparison of the past torque course with the        reference torque course, and to    -   determine an adapted pedal reference trajectory based on said        comparison.

The past torque course represents the time evolution of the input torqueapplied to the pedal, i.e., the torque as a function of time. The torquemay be determined by direct measurement using force sensors positionedin the pedal itself or at the crank connecting the pedal to its axis ofrotation. In an embodiment, the torque is determined indirectly bymeasuring the electric current produced in the generator, which isessentially proportional to the torque.

The reference torque course corresponds to the reference trajectory andis determined or derived from the reference trajectory using a vehiclemodel. The vehicle model may according to one embodiment be a bicyclemodel. This may be the bicycle model mentioned above as represented byeq. 1 or another model that, when applied, allows to induce a hapticimpression of high ergonomic quality at the at least one pedal. As shownby eq. 1, if the angular acceleration, the effective resistance torqueand the effective inertia are known, the input torque can be calculated.The effective resistance torque and the effective inertia are known asmodel parameters, which may or may not be related to an actual vehiclewhich uses the pedal drive system. The effective resistance torque maybe modeled using a variety of measured or indirectly deduced variablesas input.

In an electric vehicle, the pedal(s) and the generator connected theretodo not contribute much to the effective inertia I_(eff) and, since thereis no mechanical coupling to a driven wheel, the effective (mechanical)inertia as such is rather small. However, it is possible to use eq. 1 asa model equation, where the effective inertia is “simulated” by afeedback torque. I.e., given a known input torque T_(c), a resultingangular acceleration is calculated based on a “simulated” or “virtual”effective inertia, and this angular acceleration is used for the adaptedreference trajectory.

In one embodiment, the ratio of the pedal cadence and the angular speedof a driven wheel is used to calculate a gear ratio, which in turnallows calculation of the effective inertia. Once the referencetrajectory is determined, the resistance torque is adapted so that thepedal is guided towards or along the reference trajectory. As a result,the haptic feel for the user corresponds to a mechanical bicycle havingan effective inertia equal to the simulated inertia.

Likewise, it is possible to use the effective resistance torque as amodel parameter, and to display any driving situation or a “virtualworld” via the reference trajectory and feedback torque.

For instance, it is possible to simulate an air resistance and/or aslope of a track on which a vehicle is going. These additionalresistances may correspond to an actual situation of a vehicle which isdriven by the pedal drive system, in which case (air) speed and slopecan be determined directly by sensor measurements or can be determinedindirectly, e.g. by calculating an (air) speed from the rotationfrequency of a driven wheel. GPS measurements and maps also allow toestimate a slope which can be input into the model calculation. However,the abovementioned influences may also be simulated when using the pedaldrive system in a stationary training apparatus.

Since the effective inertia and the effective resistance torque can beseen as parameters in a model equation, from which it is possible tocalculate the angular acceleration, it is also possible to use the sameparameters in the same equation to calculate a reference torque from theangular acceleration. The angular acceleration is either given directlyby the reference trajectory or can be calculated, e.g. if the referencetrajectory represents the angular velocity (cadence) by calculating thetime derivative. Thus, it is possible to calculate a reference torquefrom the reference trajectory, which represents the “expected” pedalingbehavior of the user. This reference torque is a theoretical inputtorque which the user would have to apply to keep the pedal motion onthe reference trajectory if he was using e.g. a mechanical bicycle withthe same effective inertia and effective resistance torque. However,since the haptic renderer tries to adapt the movement of the pedal tothe reference trajectory, irrespective of the actual input torque, thisinput torque can be different from the calculated reference torque.

It should be noted that the reference torque course can be determinedbefore or after the past torque course is determined, or evensimultaneously in corresponding embodiments.

Once the reference torque course for the predefined sampling time hasbeen calculated, it is compared with the past torque course for thissampling time. If the comparison shows that the past torque course isidentical to the reference torque course (possibly except for negligibledifferences), the adapted reference trajectory may be unaltered. If thecomparison shows that there are considerable differences, there areseveral possible embodiments as to the further control. One possibilityis to use the past torque course as the basis for calculating a newreference trajectory, which in turn may be based on a vehicle model,e.g. using eq. 1. In this context, is also possible to base the newreference trajectory on an extrapolation of the input torque into thefuture. An analysis of the past torque course may be performed e.g. byidentifying a non-oscillatory (e.g. linear or constant) component andperiodic components. This would correspond to a “modified” Fourieranalysis. For the future development of the input torque, thenon-oscillatory component could be extrapolated and the periodiccomponents could be added. Of course, other extrapolation techniques arepossible. Any such extrapolation may reach into the future for arelatively small interval, like a few milliseconds or a few degrees ofpedal arm travel. However, the interval may be larger, e.g.corresponding to a full 360° rotation of the pedal arm. In any case, thetransition between the old reference trajectory and the adaptedreference trajectory usually should be smoothened using suitablemathematical methods for trajectory generation such as splines, NURBS,Bezier curves, e.g. so that the angular position and its derivatives arecontinuous functions. The measurements of the above-mentioned courseswill usually be noisy. Therefore, methods of digital signal processinglike filtering may be applied, e.g. low pass filtering, i.e.,mathematically speaking, elimination of high-frequency components.

Particularly, but not limited thereto, in the context of theabove-mentioned embodiment, it is preferred that the inertia modeleruses a vehicle model which includes an effective inertia at the at leastone pedal. In case of a rotational movement of the at least one pedal,the effective inertia is an effective rotational inertia. In anembodiment, the effective inertia may be a function of a virtual gearratio. I.e., in a model calculation, a resistance torque and angularvelocity at a driven wheel are modified (multiplied or divided,respectively) by the virtual gear ratio to determine the resistancetorque and the angular velocity at the pedal. The correspondingparameters at the driven wheel do not have to correspond to real,physical values, but can be modified or can be completely artificial. Inparticular, the effective inertia may be a factor that connects theangular acceleration to the total torque at the pedal (see e.g. eq. 1).It should be kept in mind, though, that the effective inertia of themodel has to be simulated and presented at the pedal to the user via thefeedback torque generated by the haptic renderer. Thus, the effectiveinertia of the vehicle model can also be referred to as a “virtualinertia” or “virtual effective inertia”. The virtual gear ratio may be aparametric curve using e.g. vehicle speed and/or pedaling torque etc. asa variable.

According to a further embodiment, the inertia modeler is configured toadapt the virtual gear ratio. This adaption may be performed in responseto a user input or automatically, e.g. in order to keep the resistancetorque and/or the angular velocity (or cadence) within a predeterminedrange.

In a further embodiment, the inertia modeler is configured to adapt thepedal reference trajectory so that the average pedal cadence convergesto a preferred cadence value. The average pedal cadence can becalculated by averaging the pedal cadence over time, over crank angleetc. In this embodiment, the inertia modeler adapts the referencetrajectory so that the average pedal cadence approaches the preferredcadence value. Once close, the inertia modeler (in collaboration withthe haptic renderer that controls the feedback torque) keeps the actualaverage cadence close to the preferred cadence. For instance, when theuser starts operation of the pedal drive system, the average cadence (orangular velocity) of the reference trajectory may initially, immediatelyafter the pedal has started to move, be increased linearly so that itapproaches the preferred cadence value rather quickly. As the preferredcadence value is approached, the average cadence may change from alinear increase to an exponential approach of the preferred cadence.Once the preferred cadence value has been reached and the user tries toexceed the preferred cadence value or other limits (like a maximum inputtorque that could be mechanically harmful), it is possible to change thefeedback torque by increasing or reducing it such that the hapticfeedback signals to the user to reduce the average cadence, or not toexceed an upper torque limit, or any other given limit.

In a simpler embodiment of the pedal drive system, where the referencetrajectory is not adapted in response to the input torque, the inertiamodeler may simply adapt the reference trajectory so that the averagecadence is kept or converges towards the preferred cadence value.

This preferred cadence value may be input by the user. According to oneembodiment, the control unit is configured to automatically adjust saidpreferred cadence value based on at least one state variable of thevehicle and/or the user. For example, the inertia modeler may beconfigured to make this (usually small) automatic adjustment. Examplesfor state variables of the vehicle include vehicle speed or a slope ofthe vehicle track. State variables of the user may be measured or beinput by the user. The adjustment can be performed according to aparameterized model for preferred cadence. The display of the mobiledevice or a parameterization tool of the bicycle dealer allows to setthe values of the parameters. In a further embodiment, the control unitis adapted to learn and (slightly) modify the preferred cadenceautomatically.

In one embodiment, the control unit is configured for controlling thefeedback torque by iteratively performing the following steps:

-   -   determining a pedal state variable, representing a motion of the        pedal;    -   calculating the difference between the determined pedal state        variable and a corresponding state variable derived from the        pedal reference trajectory; and    -   adapting the feedback torque based on the difference.

The basic idea of this embodiment is to detect any deviation from thereference trajectory and to adapt the feedback torque in order toeliminate or at least diminish the deviation. According to anembodiment, the above-mentioned steps are performed by the hapticrenderer. In a first step, a pedal state variable, which representsmotion of the pedal, is determined. This may be, in particular, theangular position, the angular velocity and/or the angular accelerationof the pedal. In this context, the angular position also “represents amotion” in that it is due to a motion of the pedal starting from a knownstarting position. The pedal state variable may also be an integral orrather a sum over several values measured over a (time or crank angle)interval, like the sum over the angular positions measured over the lastfew milliseconds or the like. The pedal state variable may be measureddirectly via appropriate sensors or may be calculated according tosensor measurements.

The determined pedal state variable represents the actual state of thesystem, while a corresponding state variable, which can be derived fromthe reference trajectory, represents the setpoint of the system. In anext step, the difference between these two state variables iscalculated. It should be noted that more than one state variable couldbe considered. For example, the difference for the angular position andthe difference for the angular velocity could be considered and thesedifferences could be combined e.g. in a weighted way.

In the next step, the feedback torque is adapted based on thedifference. For instance, if the difference is zero or negligible, thefeedback torque may remain unchanged. If, however there is anon-negligible difference, this indicates a deviation from the referencetrajectory, which must be corrected by an increase or decrease of thefeedback torque. In a simple, but usually effective embodiment, thechange in the feedback torque may be proportional to the difference. Inother words, the difference is multiplied by an appropriate factor todetermine the change of the feedback torque. If several differences areconsidered, each difference may have a corresponding factor and theadaption of the feedback torque may be considered as a “linearcombination” of the differences. However, there may be moresophisticated methods to determine the feedback torque, for example byusing some convergence criterion, which also takes into account not onlyif there is a difference between the pedal state variables, but also ifthis difference is currently decreasing or increasing and, if it isdecreasing fast enough.

Normally, the reference trajectory itself remains unchanged while thesesteps are performed. However, an adaption of the reference trajectorymay be performed in between, which will of course influence thedetermination of the state variable in the second step.

While the above-mentioned embodiment relies on monitoring one or severalpedal state variables, which represents motion of the pedal, thefeedback torque may also be adapted based on the input torque. In thisembodiment, the control unit is configured for controlling the feedbacktorque by iteratively performing the following steps:

-   -   determining the input torque;    -   calculating the difference between the determined input torque        and a corresponding reference torque derived from the pedal        reference trajectory; and    -   adapting the feedback torque based on the difference.

As already mentioned above, a “theoretical” input torque can becalculated from the reference trajectory using a vehicle model, e.g. byapplying eq. 1. The angular acceleration is easily derived from thereference trajectory, and with the effective inertia and the effectiveresistance torque known e.g. as model parameters, an input torquecorresponding to the reference trajectory can be calculated, which ishere referred to as the reference torque. Most of the time, the actualinput torque is different from the reference torque, which necessitatescompensating the difference by increasing or decreasing the feedbacktorque. However, it should be borne in mind that even if the actualinput torque was equal to the reference torque (i.e. if the differencewas always zero), the feedback torque may have to be adapted over timein order to guide the pedal along the reference trajectory.

Irrespective of whether the adaption of the feedback torque is based ona difference of state variables or on a difference of torques, it may beperformed more or less regularly at short intervals. In terms of crankangle, the adaption may, in corresponding embodiments, occur at mostevery 5 degrees, at most every 2 degrees or at most every degree. Interms of time, the adaption may occur at most every 10 ms, at most every5 ms, at most every ms or at most every 500 ns. It should be noted thata current controller collaborating with the haptic renderer may work atmuch higher frequencies of kHz to fractions of MHz.

In another embodiment, said at least one pedal reference trajectorycomprises at least one alternating trajectory component having a periodlength that corresponds to a pedal revolution or half a pedalrevolution. As already mentioned above, the angular velocity of thepedal in a mechanical bicycle is never exactly constant, but shows aripple, i.e., an oscillation about a mean value. This results from thefact that a user can apply a torque to the pedal that depends on thepresent crank position. For example, if the crank is approximatelypositioned horizontally, it is easy for a user to apply a relativelylarge torque, while in other positions, the torque is rather limited.These variations of the torque also influence the angular velocity.Therefore, if such an oscillation or ripple is reproduced in a pedalreference trajectory, the user experiences a haptic sensation that issimilar to that on a mechanical bicycle. The oscillation may berepresented by the above-mentioned alternating trajectory component,which may be added to a constant or slowly changing “average” value.Normally, with two pedals, the user performs a more or less symmetricpedaling motion. In this case, the period length corresponds to half apedal revolution. It is conceivable, though, that the motion isasymmetric, i.e., the motion of the right pedal does not correspond tothe motion of the left pedal. Such asymmetric motion may be useful forrehabilitation training applications. In such a case, the period lengthcorresponds to one pedal revolution. The alternating trajectorycomponent may be periodic at least over a plurality of oscillations.However, it is possible that the amplitude and/or waveform of thealternating trajectory component changes with each oscillation. Ingeneral, the waveform does not have to be sinusoidal, corresponding to asingle wavelength, but may comprise “upper harmonics”, i.e., componentswith smaller wavelength. The amplitude of the alternating trajectorycomponent is in an embodiment less than 10% of the current mean value ofthe trajectory (i.e., the value about which the trajectory isoscillating).

In one embodiment, the amplitude and the waveform of the alternatingtrajectory component depend on at least one state variable of a vehicleand/or the pedal. Examples for such a state variable include pedalposition, cadence, speed of a vehicle driven by the pedal drive systemor time (e.g. time that has passed since the beginning of operation ofthe drive system, or since the first half pedal revolution has takenplace). As mentioned above, in a mechanical bicycle, the amplitude ofthe ripple decreases with increasing speed or with increasing gearratio, respectively. In a bicycle with electronic transmission, theinertia modeler allows for a similar behavior by reducing the amplitudeof the alternating trajectory component in a similar way as is knownfrom power-assisted or non-power-assisted bicycles with a mechanicaldrivetrain. Likewise, the inertia modeler may decrease the amplitude ofthe ripple with increasing cadence.

According to another embodiment, the control unit comprises multiplepedal reference trajectories, which are alternatively selectable. I.e.,several pedal reference trajectories are stored, e.g. in a library, andone of these may be selected either manually by the user orautomatically. In particular, the haptic renderer or the inertia modelermay comprise the multiple reference trajectories.

The haptic renderer may be configured to select one of said multiplereference trajectories automatically based on a trajectory selectionsignal. This selection signal may be input by the user or it may begenerated automatically. Such a signal may originate from a sensor thatsenses cadence and/or pedal torque, the slope of a track the vehicle ispresently on, the drive torque on a driven wheel, the vehicle speed orother. To this respect, multiple reference trajectories for the pedal,which are selected depending on e.g. vehicle track slope, may beregarded as part of a reference plane. While a single referencetrajectory is a graph in a 2D coordinate system (the coordinates beinge.g. angular position and cadence), the reference plane is located in a3D or even higher dimensional coordinate system (the coordinates beinge.g. angular position, track slope and cadence).

As mentioned above, the inertia modeler is in an embodiment configuredto iteratively adapt the at least one pedal reference trajectory atpredetermined intervals. In further embodiments, these intervalscorrespond to less than one revolution of said pedal, in particular atmost 10 degrees, at most 5 degrees or at most 3 degrees of rotationangle of said pedal. With typical cadence values, a 10-degree-rotationangle corresponds to about 3-30 ms. Thus, the adaption may be carriedout at time intervals of about 1-30 ms. However, larger or even smallertime intervals are conceivable in corresponding embodiments. Thenecessary calculations for the adaption can be carried out on this timescale either on a local controller or by a suitable mobile computingdevice that is used to implement the inertia modeler. Thus, it ispossible to adapt the reference trajectory with high angular and/or timeresolution and the inertia modeler can adapt quickly to any changes ofthe pedaling behavior of the user.

In another aspect, an electric vehicle is provided, with a pedal drivesystem as described above, wherein an electronic transmission connectssaid generator to an electric load and/or an electric drive motor. Theelectronic transmission may comprise power electronics for the generatorand/or the drive motor and an intermediate circuitry with at least oneenergy storage device. Such an energy storage device may be a battery, afuel cell, a high-capacity capacitor and/or any other suitable currentsource. The main function of the energy storage device is to temporarilystore surplus energy from the generator. However, it may also serve as arechargeable energy source that can be charged via a power cable or, ifthe drive motor is operated as a generator during electrical braking,also surplus energy from the motor may be stored in the energy storagedevice. It is understood that such an electric vehicle has at least onedriven wheel, which is mechanically connected to the drive motor. Foreffective traction control and in an embodiment, the torque and/or theangular velocity at the driven wheel is not influenced by any ripplepresent in the torque and/or angular velocity of the pedal. In otherwords, the torque at the driven wheel is preferably constant or changesmonotonously over one pedal revolution. If the reference trajectory isdetermined based on a bicycle model, the virtual effective inertia andthe effective resistance torque may be based on real physical parametersof the bicycle. I.e., the real mass of the bicycle and the user may beused as a basis for calculating the virtual effective inertia, while airresistance (based on the current speed of the bicycle), slope of thedriving surface and other parameters may be used as a basis forcalculating the effective resistance torque.

Possible embodiments of the above-mentioned vehicle correspond toembodiments of the inventive pedal drive system.

In yet another aspect, a training apparatus is provided, with a pedaldrive system as described above. In such a training apparatus, theenergy generated in the generator is usually just dissipated andconverted into heat. Normally, there is no driven wheel, although it isconceivable that the generator is coupled to a drive motor, which inturn is coupled to a flywheel. In contrast to a bicycle, there are noreal physical parameters on which the virtual effective inertia and theeffective resistance torque can be based (although one could calculatethe effective inertia based on the mass of the apparatus and the user).Commonly, if a bicycle model is used to determine the effective inertiaand the resistance torque, these parameters can be chosen more or lessarbitrarily. In particular, the resistance torque can be modeled basedon a “virtual” track.

Possible embodiments of the above-mentioned training apparatuscorrespond to embodiments of the inventive pedal drive system.

In another aspect of the invention, a method of operating a pedal drivesystem for generating electrical power from muscle power of a user isprovided, with at least one pedal and an electric generator, which isconnected mechanically with said at least one pedal, wherein a feedbacktorque, applied at said pedal, is controlled based on at least one pedalreference trajectory. The generated electrical power may be used locallyor may be fed into the electrical grid.

These terms have been explained in detail above in context with theinventive pedal drive system. It is understood that in the context ofthis method, the pedal drive system may comprise a control unit, whichin turn comprises a haptic renderer, and the feedback torque may becontrolled by the haptic renderer of the control unit. Possibleembodiments of the above-mentioned method correspond to embodiments ofthe inventive pedal drive system.

According to yet another aspect, an electric drive system for a vehicleis provided, which is operated with muscle power and comprises at leastone pedal, an electric generator, connected mechanically with said atleast one pedal, an electric drive motor, connected electrically withsaid electric generator, and a drive controller, wherein said drivecontroller is configured to

-   -   determine a maximum acceleration value of the vehicle according        to a predefined relationship based on at least two current        vehicle state parameters,    -   determine a desired vehicle acceleration based on a pedaling        performance of a user, and    -   operate the electric drive motor so that the vehicle        acceleration is limited by the determined maximum acceleration        value.

Unless otherwise noted, like terms correspond to those explained abovein context with the inventive pedal drive system.

The electric connection between the motor and the generator may beachieved by an electronic transmission as mentioned above, which maycomprise power electronics for the generator and/or the motor and anintermediate circuitry with at least one energy storage device. It isunderstood that part of the electrical power for the drive motor may betaken from the energy storage device, which may have been chargedexternally by a connection to the power grid. In a vehicle, at least onedriven wheel is mechanically connected to the drive motor.

The drive controller, which may be implemented as hardware and/orsoftware, is configured to determine a maximum acceleration value of thevehicle. This maximum acceleration value is an acceleration limit whichis not to be exceeded. Reasons for such limitation may pertain tooperating safety of the vehicle (e.g. preventing slip of a drivenwheel), power management of an energy storage device, legal speedlimits, etc. It should be noted that the maximum acceleration value canbe negative in some cases, thus representing a deceleration. The maximumacceleration value is not fixed, but depends on at least two currentvehicle state parameters (wherein the term “current” is to be understoodto include embodiments where the parameters are used with some timedelay that is inevitable and/or considered to be irrelevant). In otherwords, the maximum acceleration value can be represented by a plane in a3D coordinate system with two coordinate axes representing the twovehicle state parameters. If it depends on more than two vehicle stateparameters, it can be represented by a hyperplane in a higher dimensioncoordinate system.

The drive controller may either calculate the maximum acceleration valuein real time based on a corresponding formula or it may read the valuefrom a lookup table, database, library, etc. The formula, the lookuptable, database, or the library, respectively, represent the predefinedrelationship according to which the maximum acceleration value isdetermined. The vehicle state parameters are representative of a currentvehicle state. They may e.g. pertain to the motion of the vehicle, itslocation or the properties of the track. In general, there are manypossibilities for selecting such parameters, as long as there is areasonable connection between a given parameter and an accelerationlimit.

Also, the drive controller is configured to determine a desired vehicleacceleration based on a pedaling performance of a user. In general, thiscan be done before, after or simultaneously with determining the maximumacceleration value. The concept is that the pedaling performance of theuser is “interpreted” as a desire to accelerate or decelerate. Thepedaling performance may be assessed e.g. based on angular velocity (orcadence), input power or input torque. According to one or severalpredefined rules, the drive controller deduces a desired vehicleacceleration from the pedaling performance.

However, this desired vehicle acceleration may only correspond to anactual vehicle acceleration if it does not exceed the maximumacceleration value. Therefore, the electric motor is operated so thatthe vehicle acceleration is limited by the determined maximumacceleration value. It should be noted, though, that in some cases themaximum acceleration value may be exceeded unintentionally, though, dueto unforeseeable influences (e.g. an abrupt change of the vehicle tracksslope, a sudden tailwind or the like). However, since the controllerusually adapts very quickly, e.g. within fractions of a second, afeasible value for acceleration is normally reached by ramping down veryfast.

According to an embodiment, the drive controller is configured to

-   -   compare a performance parameter, which is characteristic of a        current pedaling performance of the user, with a predefined        reference parameter,    -   determine the desired vehicle acceleration corresponding to the        difference between performance parameter and the predefined        reference parameter.

The performance parameter may be e.g. the power input by the user or theinput torque. This performance parameter is compared with a referenceparameter. The reference parameter may be predefined before operation ofthe vehicle starts or it may be based on past pedaling performance ofthe user. For instance, if the performance parameter is the inputtorque, the reference parameter may be the input torque during aprevious rotation of the pedal. For example, if the user has beenpedaling with a certain maximum input torque during one or severalrotations of the pedal, this maximum input torque may be used as areference parameter. If the user starts pedaling more forcefully, i.e.,if he applies more input torque, this can be interpreted as a desire toaccelerate, which is found by comparing the current input torque withthe reference parameter (i.e. the past input torque). According toanother example, the reference parameter may be a reference input power.If the current input power exceeds the reference input power, this canbe interpreted as a desire to accelerate the vehicle. It is to beunderstood that while the desired vehicle acceleration is determinedcorresponding to the difference between the performance parameter andthe predefined reference parameter, the desired vehicle accelerationdoes not necessarily depend linearly on this difference. In particular,if the difference is small, although nonzero, the desired vehicleacceleration may be determined to be zero, though.

In an embodiment, the at least two vehicle state parameters comprise atleast vehicle speed and vehicle track slope, so that the maximumacceleration value is determined as a function of at least vehicle speedand vehicle track slope. “Vehicle track slope” of course refers to theinclination of the driving surface of the vehicle. One of the ideas hereis to limit the maximum acceleration more and more as the speedincreases, which usually leads to a limitation of the vehicle speeditself. For instance, if the maximum acceleration value decreases withincreasing speed and becomes zero for a predefined “speed limit”, thismostly prevents the vehicle from exceeding this limit. The maximumacceleration value can be negative for higher speeds. In this case, thedrive motor could start to brake electrically, and hence recuperatekinetic energy. One reason for such a speed limit can be trafficregulations and/or safety precautions. Another reason may be that due toincreasing air drag, it becomes difficult to accelerate above a certainspeed without excessively draining an energy storage device.

For the same reason, it may be useful to limit the maximum accelerationwith increasing track slope. Of course, the energy consumption at thedrive motor increases with increasing track slope, even if the vehicleonly maintains a certain speed. Trying to accelerate will increase thetotal energy consumption even more so that it may have to be limited. Inthis way it is possible to limit the total drive torque required at theat least one driven wheel caused by air drag, downhill-slope force andacceleration force to a certain maximum value. Thus, the maximumacceleration value would be dependent on the vehicle speed and thevehicle track slope. Another option would be to limit the accelerationin order to prevent slipping of the driven wheel. In such a case, it isconceivable to not only include the track slope but also the frictioncoefficient between the driven wheel and the track, which may bedetermined based on GPS-based information on the track surface (asphalt,gravel, dirt etc.) and/or weather data (dry/wet/icy underground). These,however, are just examples and there are many other possibilities howthe maximum acceleration value can depend on vehicle speed and vehicletrack slope.

In one embodiment, the at least two vehicle state parameters comprise atleast speed limit information, based on the current location of thevehicle. In such an embodiment, the drive controller can be connected toa GPS module and/or may have access to a database that links the vehicleposition to a local (or national) speed limit. Thus, a speed limit asmentioned above is not static but can be determined depending on thevehicle position. As mentioned above, the maximum acceleration value maybecome zero if the vehicle speed reaches the speed limit. Alternatively,a speed limit may be input by the user or could even be determined by animage recognition software that “reads” traffic signs.

In another aspect of the invention, an electric vehicle is provided,with an electric drive system as described above.

As mentioned above, the total power for the drive motor is generally acombination of generator power, that is mechanical power by the userminus losses in the generator, gear and power electronics associatedwith the pedal generator, and power from a rechargeable energy storagedevice like a battery. Unless the energy storage device is totallydrained, there are several options how the necessary drive power can beobtained. In an embodiment, the percentage of the power generated by theuser in relation to the total required drive power is changed graduallyas a function of the current from the energy storage device. Forexample, the percentage may almost be constant (e.g. 40%) within acertain range, e.g. when the battery current is between 0 and 3 timesthe nominal current. When the battery current increases further, thepercentage may also increase steadily, e.g. according to a polynomialfunction, up to 100% (which may be reached for example when the batterycurrent is 5 times the nominal current). If the battery current becomesnegative, i.e. if energy is recuperated, the percentage of the user'scontribution to propulsion may be decreased steadily, e.g. according toa polynomial function. In any case, the percentage should not changeabruptly (i.e. contain “jumps”) as a function of the battery current.

Reference will now be made to the drawings in which the various elementsof embodiments will be given numerical designations and in which furtherembodiments will be discussed.

Specific reference to components, process steps, and other elements arenot intended to be limiting. Further, it is understood that like partsbear the same reference numerals, when referring to alternate figures.It will be further noted that the figures are schematic and provided forguidance to the skilled reader and are not necessarily drawn to scale.Rather, the various drawing scales, aspect ratios, and numbers ofcomponents shown in the figures may be purposely distorted to makecertain features or relationships easier to understand.

FIG. 1 shows a schematic representation of components of an electricvehicle 100 according to one embodiment. In particular, this may be abicycle. It is understood that for sake of clarity and simplicity, manycomponents of the vehicle 100 are not shown. The vehicle 100 comprises apedal drive system 10 and an electric drive system 20. The pedal drivesystem 10 comprises two pedals 11, which are mechanically connected by acrank 12 to an electric generator 13. While the mechanical connection isshown in simplified form, it is understood that such a connection couldfeature some kind of transmission mechanism. The electric generator 13is connected to first power electronics 14, which in turn are connectedto a control unit 30.

On the one hand, the control unit 30 receives information on theoperation of the pedals 11 via the first power electronics 14 from afirst sensor unit 40. Such information—which may also be used by thefirst power electronics 14—may in particular comprise information on aninput torque applied by a user, and angular position of the crank 12, anangular velocity (or a cadence, respectively) and/or other quantities.It should be noted that while the input torque could be measured bydedicated force sensors on either pedal, pedal arm, or gear components,which may be part of the first sensor unit 40, in this exemplaryembodiment, the input torque is determined by measuring the current fromthe generator 13, which, for some types of electrical machines, e.g., DCmachines or PMSM machines, is proportional to the input torque.Quantities pertaining to the position of the crank 12 may be determinedby the first sensor unit 40, which comprises an angular encoder.

On the other hand, the control unit 30 can send a control signal to thefirst power electronics 14 in order to control a feedback torque that isapplied to the crank 12 and the pedals 11 by the generator 13. Inparticular, the control unit 30, which may at least partially beimplemented in software, comprises a haptic renderer 31, which isconfigured to control the feedback torque based on a predefined pedalreference trajectory. Such a pedal reference trajectory, which will bediscussed in more detail below, may for example represent a nominalvalue for the cadence (or angular velocity) as a function of the angularposition. In other words, the haptic renderer 31 controls the feedbacktorque so that the actual cadence corresponds to the referencetrajectory. Alternatively, the reference trajectory could represent anominal value for the angular position and/or any of its timederivatives. Of course, the haptic renderer 31 either comprises or isconnected to a memory device (not shown), in which the referencetrajectory is stored. Usually, the feedback torque is a counter torque,i.e., a torque that counteracts the input torque applied by the user.One could say that the counter torque and the reference trajectory, onwhich it is based, simulate a “virtual” inertia of the vehicle 100. Theactual, physico-mechanical inertia of the pedals 11, the crank 12 andthe generator 13 is comparatively low, so that the haptic feeling of auser operating the pedals 11 largely depends on the feedback torque. Ifpossible, the feedback torque is generated by operating the generator 13normally, i.e., as a generator. However, the feedback torque may also begenerated by operating the generator 13 as a motor. This operation modemay also be employed to generate a supporting torque, i.e., a torquethat acts in the same direction as the input torque applied by the user,or a hold torque to e.g. support the weight of the leg and foot beforestarting. The control unit 30 also comprises an inertia modeler 32,which is configured to iteratively adapt the reference trajectory whichis then provided to the haptic renderer 31. Operation of the inertiamodeler 32 will be described in detail below.

The control unit 30 is also connected in a wired manner or wirelessly toa human-machine interface 60, which may be integrated into the vehicle100 or may be a mobile device like a smartphone or smartwatch, a PDA ora tablet. A user may input certain parameters via the human-machineinterface 60 or may just specify his identity, whereafter certainparameters are automatically determined. Of course the human-machineinterface 60 may also serve as a display for the user, where currentvalues of vehicle speed, cadence, pedal power, etc. are shown, and/orallow remote diagnosis of the vehicle 100.

The pedals 11, the generator 13 with the first power electronics 14 andthe control unit 30 are also part of an electric drive system 20 of thevehicle 100. This electric drive system 20 further comprises an electricmotor 21, which is coupled to second power electronics 22, which in turnare connected to the control unit 30. The electric motor 21 ismechanically connected to at least one driven wheel 23. It may either bedirectly connected to the hub of the driven wheel 23 or via atransmission mechanism. The second power electronics 22 are alsoelectrically connected to the first power electronics 14 and to anenergy storage device 50 for energy exchange. The energy storage device50 may, e.g., be a rechargeable battery, a capacitor, or a combinationof both. Also, a current source like a fuel cell may be combined with anenergy storage device like a battery with low impedance. Normally,energy will be transferred from the first power electronics 14 and/orthe energy storage device 50 to the second power electronics 22.However, the electric motor 21 may also be employed as a generator, e.g.when the vehicle 100 is going down a slope, so that energy can betransferred from the second power electronics 22 to the first powerelectronics 14 and/or to the energy storage device 50.

The control unit 30 further comprises a drive controller 33, whichcontrols the second power electronics 22 in order to achieve a certaindrive torque and/or a certain angular velocity or angular accelerationat the driven wheel 23. Operation of the drive controller 33 will bedescribed in more detail in the following. The control unit 30 alsoreceives information on the electric motor 21 or the driven wheel 23 viathe second power electronics 22 and/or a second sensor unit 41. Suchinformation—which may also be used by the second power electronics22—may refer to the drive torque, the angular velocity or othercharacteristic quantities.

Alternatively, the control unit 30 could receive this informationdirectly, i.e., not via the second power electronics 22.

It should be noted that while the first and second sensor unit 40, 41are each shown as a single, localized device, each of them can be agroup of sensors that are spaced apart. Beside this, the vehicle maycomprise a third sensor unit 42, which is neither located near thegenerator 13 nor near the electric motor 21. Sensor unit 42 may belocated at any suitable location on the vehicle 100 or the user.Examples for such sensors are GPS sensors, inclination sensors, heartrate sensors for the user, etc. The sensor units 40, 41, 42 can beconnected by wires or wirelessly. They can be connected to a serial busso that bidirectional information exchange, e.g., so thatre-parameterization is possible.

Referring to FIG. 2 , a method for controlling the feedback torqueaccording to a reference trajectory will be described. The method isconducted by the haptic renderer 31. After starting at step 200, areference trajectory, which may be provided by the inertia modeler 32 orby a trajectory library of the control device 30 (not shown, butdiscussed in more detail in the following), is received at step 201. Instep 202, one or several pedal state variables are determined, which maybe the angular position, a sum over angular positions, the angularvelocity or the angular acceleration of the pedals 11 (or generator 13,which, normally, is connected to the pedals 11 with a fixed gear ratiowhich can be known to the control unit 30. A variable gear ratio is anoption.). In step 203, the corresponding state variable(s) are derivedfrom the reference trajectory. If necessary, numeric integration ornumeric differentiation can be employed to determine the respectivestate variable. For instance, if the pedal state variable is an angularvelocity and the pedal reference trajectory defines an angularacceleration, the angular position first has to be calculated byintegration.

In step 204, the difference between each actual state variable and thecorresponding state variable derived from the pedal reference trajectoryis calculated. In step 205, it is checked whether any of the differencescalculated in step 204 is relevant, i.e. non-negligible. If so, thefeedback torque is adapted in step 206 and the procedure is repeatedwith step 202. The feedback torque may be increased by an amount that isa linear combination of the differences calculated in step 204. I.e., ifthere is only one difference, the increase of the feedback torque isproportional to this difference. If there is no relevantdifference—which will be rarely the case—the procedure immediately goesback to step 202 without adapting the feedback torque. Usually, methodscommon in signal processing for noise reduction are applied before thecalculation in step 204 in order to get the pedal state variables ingood quality.

It should be noted that some steps that are shown sequentially maytemporally occur in parallel, i.e., at the same time. E.g., steps 202and 203 may be performed in parallel during the same time interval. Suchparallelization can help to increase the frequency of the feedbacktorque adaption.

Now, with reference to the flow diagram of FIG. 3 , the adaption of areference trajectory by the inertia modeler 32 will be described. Afterthe start in step 300, the inertia modeler in step 301 reads orcalculates initial parameters, like an effective inertia, an effectiveresistance torque etc. These parameters may be stored in the memorydevice. The initial parameters may also be determined based on a userselection or may be calculated based on sensor readings. In step 302,the inertia modeler calculates a reference trajectory using a vehiclemodel. If there is no data available on the pedaling behavior of theuser (such as for example the input torque), a standardized referencetrajectory is used. Here, it is also possible that the referencetrajectory is selected from multiple reference trajectories stored inthe trajectory library of the control unit 30. Next, in step 303, thepedal is guided along the reference trajectory. That is, the referencetrajectory is provided to the haptic renderer 31, which in turn controlsthe feedback torque accordingly, e.g., as described with reference toFIG. 2 . At the same time, the input torque T_(c), or rather itsevolution over time or angular position, is measured and stored forfuture reference. As shown with reference to FIG. 2 , step 303 actuallycontains a loop, which may be performed for e.g. a few millisecondsbefore the method continues with step 304. In this step, it is checkedwhether the user has stopped pedaling forward, which may be detectede.g. by a relatively abrupt decrease of the input torque T_(c). Itshould be noted that such a check could also be included in the loop ofFIG. 2 . If the user has stopped pedaling forward, the method continueswith step 305 and enters a freewheeling mode. In this mode, the pedal 11is no longer guided along a reference trajectory (which may otherwisecontravene the user's will), but it is allowed to decelerate and stop oreven to be moved backwards. This process of slowing down can happen in atorque control mode, or according to a newly calculated or retrievedreference trajectory which governs the slowing down process. In contrastto a mechanical bicycle, where the pedal 11 is either completely coupledor decoupled, it is possible to work in an “intermediate” mode, wherethe pedal 11 is partially coupled. This means that as the pedal 11 isdecelerating, the user still feels some resistance torque from theelectric generator 13, while kinetic energy from the user's legs isrecuperated. If in step 304 it is being detected that the user moves thepedal 11 backwards, the generator 13 is operated as a motor to assistthe intended motion of the pedal. This state of operation may be used tomove the pedal 11 into an ideal starting position. There, aholding/clamping torque can be applied e.g. if a brake lever is pulledby the user.

If the user has not stopped pedaling forward, the method continues withstep 306, where parameters are updated. Such parameters may include the(virtual) effective inertia and the effective resistance torque. Thelatter may depend on a vehicle tracks slope and/or a vehicle speed(which influences the air drag). In particular, it is possible to adaptthe virtual gear, either automatically or in response to a user input.For instance, the virtual gear may be adapted so that the user isencouraged to reach a preferred cadence value (or is deterred fromdeviating from such a preferred cadence value).

During step 303, the input torque has been recorded in order to obtain apast torque course of the input torque at the pedals 11. This torquecourse represents the time evolution of the torque over a certainsampling time, which may be e.g. between 1 and 100 ms. Using a vehiclemodel with an appropriate equation of motion (e.g. eq. 1), a referencetorque course is calculated, which is derived from the pedal motionrepresented by the reference trajectory. This reference torque courserepresents the “expected” input torque during the sampling time. In step307, the past torque course is compared with the reference torquecourse. If there is a relevant difference, which will usually be thecase, the reference trajectory is adapted in step 308. Here, it isoptionally possible to extrapolate the past torque course into thefuture and use the equation of motion to calculate a referencetrajectory corresponding to this extrapolation. However, the transitionbetween the “old”, unadapted reference trajectory and the “new”, adaptedreference trajectory usually is smoothened by suitable mathematicalmethods, e.g. using splines. According to an embodiment, the adaption ofthe reference trajectory is performed at relatively short intervals,like every 1-100 ms or every 1°-10° of rotation of the pedals 11. Oncethe reference trajectory has been adapted, the method goes back to step303. In the (rare) case that there is no relevant difference between thepast torque course and the reference torque course, the methodimmediately goes back to step 303 without adapting the referencetrajectory.

It should be noted that in a simplified embodiment, the input torque maynot be measured in step 303 and the check at step 307 may be omitted. Inthis case, the reference trajectory is independent of the pedalingbehavior of the user. Of course, the adaption in step 308 in this caseis also independent of the input torque. As in FIG. 2 , some steps thatare shown sequentially may be performed in parallel, i.e. at the sametime. This may be done asynchronously or synchronously, depending on theactual implementation of the embodiment. E.g., temporally, step 306 maytake place in parallel to step 303.

FIG. 4 , by way of example, illustrates the development of an inputtorque and an angular velocity as a function of the crank angle. Thefull width of the diagram represents a 360° rotation of the crank 12.The input torque during this period has two peaks within this interval,which is due to the presence of two pedaling legs and two pedals 11,which move with an approximate or exact 180° phase shift. The data shownhere represent one revolution of the cranks 12, which are 180° apart.The input torque T_(c) for a first revolution is roughly sinusoidal andin this case has maximum values close to or at 90° and 270° pedalposition, and minimal values at 0°, 180° and 360°. The angular velocityor cadence for this revolution is proportional to the integral of thetotal torque, which apart from the input torque comprises the feedbacktorque applied by the haptic renderer 31. The cadence is also roughlysinusoidal, and has a 45° phase shift with respect to the input torque.The cadence could be used as a reference trajectory for the followingrevolution of the crank 12. As indicated by the horizontal line, thecadence oscillates about an average value. If the cadence is consideredas a reference trajectory, this reference trajectory would be composedof a non-oscillatory (e.g. constant or linear) component and analternating trajectory component or “ripple”. Such a structure can alsobe used in a case where the inertia modeler only partially bases thereference trajectory on the pedaling behavior of the user, but uses amore or less realistic model function. The alternating trajectorycomponent or ripple shown here is roughly sinusoidal. However, it alsocomprises components having shorter wavelengths, which may be regardedas upper harmonics. In the present case, the average value of theangular velocity is constant over the whole revolution of the crank 12,but it could also be changing more or less slowly.

FIG. 5 illustrates the adaption of the reference trajectory in responseto the input torque T_(c) applied by the user. It should be noted thatall quantities here are shown as a function of the crank angle. Given asa function of time, the corresponding curves would be deformed, due tothe non-constant angular velocity. In the diagram on the left,representing step n, the cadence cad_(n−1) of the reference trajectoryis alternating about a constant average value. The index “n−1” indicatesthat this reference trajectory was calculated based on the previous stepn−1. It should be noted that since the haptic renderer 31 guides thepedal 11 along the reference trajectory, the cadence cad_(n−1) of thereference trajectory is more or less identical to the actual cadence.The bold dotted line indicates a reference torque T_(ref, n−1), which iscalculated from the cadence cad_(n−1) using a vehicle model. However,the actual input torque T_(c, n) during step n normally does notcorrespond to the expected value. In the shown example, it has a largervalue over the entire 360° revolution. Due to the feedback torqueapplied by the haptic renderer and due to the virtual inertia applied,this larger input torque does not (immediately) lead to an increasingcadence, though. However, the increased input, which is indicated by theshaded area, still leads to additional energy generation in thegenerator 13, which may either be transferred to the motor 21 or storedin the energy storage device 50.

Now, in the transition from the left to the right diagram (whichrepresents the future crank angle), the reference trajectory is adaptedas in step 308 of FIG. 3 . Basically, the vehicle model is applied andallows the derivation of an adapted reference trajectory. Due to thefact that T_(c,n) is higher than T_(ref,n−1) (the difference being theshaded area) the wish of the user to accelerate is detected. So theaverage cadence of the new reference trajectory, cad_(n) accelerates.

As indicated by the fine full line in the diagram on the left, the inputtorque can optionally be extrapolated, which corresponds to the bolddotted line in the diagram on the right hand side. Here, theextrapolated input torque T_(c,n,_extrapolated) can be considered as thenew reference torque T_(ref,n), which can be used to calculate thecadence cad_(n) of the new reference trajectory. As can be seen, due tothe increased input torque in step n, the cadence cad_(n) is increasingand in particular has an increasing average component (in addition to analternating component). The transition between the cadence in step n andthe cadence in step n+1 may be optionally smoothened by appropriatemathematical methods e.g. using splines. By way of example, the inputtorque T_(c, n+1) during step n+1 is shown, which again exceeds thereference torque T_(ref,n). For the next step n+2, the input torqueT_(c, n+1) may again be extrapolated T_(c,n+1,extrapolated) as indicatedby the thin solid line and can be used to calculate the cadence for thenext reference trajectory.

FIG. 6 illustrates the time evolution of the cadence after startingoperation of the vehicle 100. Here, the time since the start ofoperation may serve as a trajectory parameter for the inertia modeler32. As can be seen in the diagram, the cadence of course starts fromzero and within a few seconds converges to a preferred cadencecad_(pref) (in this example, 60 rpm), which may be a default value ormay be determined by a user input. It represents a cadence that isconsidered most efficient and/or most convenient for the user. Thecadence starts to increase according to a predefined angularacceleration b_(default), which may be determined by a user input. Inany case, this acceleration is limited for security reasons by a maximumallowed acceleration b_(max). As indicated by the fine dashed line, thecadence comprises a relatively slowly changing “average” component andan alternating component or ripple, which is added to the averagecomponent. Optionally, the alternating component may be set to be zerofor an initial time period e.g. during the time needed for the firsthalf pedal revolution before it takes on a relatively large amplitude.After that, as the average component increases and approaches thepreferred cadence, the amplitude of the alternating component decreases.In other words, the cadence becomes more and more constant. Thiscorresponds to the behavior of a mechanical bicycle, which allowssteadier pedaling at higher velocities, partially as a result of ahigher gear ratio and higher effective inertia. If the referencetrajectory is adapted according to the pedaling behavior of the user,e.g. as described with reference to FIG. 3 , it may be not be possibleto realize an idealized evolution of the cadence as shown in FIG. 6 ,since the user has some influence on the cadence. However, even in sucha case, the inertia modeler influences the pedaling behavior, e.g. byadapting the virtual gear, so that the user is encouraged to pedalslower or faster. It should be noted that as the cadence increases inFIG. 6 , the angular velocity of a driven wheel usually also increases,although usually at a different rate. Since there is no mechanicaltransmission between the generator and the electric motor, the operationof the electric motor, connected with the driven wheel, is largelyindependent of the pedaling behavior. In particular, the angularvelocity of the electric motor in one embodiment comprises no ripple atall. Although there is no mechanical transmission, the fact that thecadence is more or less constant after a few seconds, while the vehicle100 may still be accelerating, can be regarded as a result of a changingvirtual gear ratio, which in turn influences a virtual inertia. Itshould be noted that while in a mechanical bicycle, there is a limitednumber of gear ratios, the virtual gear ratio can be adjustedcontinuously, which results in the possibility of a mostly constantcadence. The preferred cadence cad_(pref) can be selected according to auser input, but it may also be adjusted automatically by the controlunit 30 (e.g. by the inertia modeler 32) according to a state variableof the vehicle or the user.

FIG. 7 shows the dependency of the average input torque as a function ofthe average cadence. Here, both averages may be e.g. over time or overcrank angle. Due to the limits of the mechanical stability of the pedals11, the crank 12 and a gear (if present) and/or the electrical limits ofthe generator 13, the input torque has an upper limit T_(max). Also, forseveral reasons such as voltage limitation, inverter topology,mechanical integrity of rotating components in the generator or itsgear, the cadence has an upper limit cad_(max). The preferred cadencecad_(pref) (indicated by the vertical thin dashed line) of course isbelow this upper limit. When the cadence is zero, i.e., the user is notpedaling, the (average) torque may either be zero or, in an alternativeembodiment, may have a finite value T_(hold), which allows the user tostart pedaling with a haptic feeling of initial resistance. In eithercase, as the cadence increases, the torque increases in such a way thatstarting acceleration of the pedal(s) is limited, and then the torquestarts to decrease according to a “stiffness” of the pedaler which isindicated by the declining thin dashed line. This stiffness may beselected according to a user input, or it can be learnt by thecontroller through observation during vehicle operation. It should benoted that when the user exceeds any torque or speed limit (indicated bythe bold dashed lines), the torque may change, i.e., increase ordecrease, to a value that feels uncomfortable for the user, so that heis deterred from exceeding the corresponding limit. Within the mentionedlimits, in the operating range, the control unit guides the user along(or towards) the reference trajectory and the average cadence of thereference trajectory can be adapted stepwise so that the preferredcadence is always reached within a reasonable time (e.g. withinseconds).

As mentioned above, the drive controller 33 controls the second powerelectronics 22, whereby a drive torque and/or an angular velocity of thedriven wheel 23 is controlled. In particular, the drive controller 33can be configured to limit a vehicle acceleration. This limitation isillustrated by FIG. 8 , which is a diagram showing a reference plane fora maximum acceleration value. As can be seen, the diagram is a 3Dcoordinate system, with one axis representing the current vehicle speed,the second axis representing the vehicle track slope, i.e., the slope ofa track or driving surface on which the vehicle 100 is running, and thethird axis representing the maximum acceleration value. Duringoperation, the current vehicle speed can be easily determined bymultiplying the current angular velocity of the driven wheel 23 by itscircumference. The vehicle track slope can be determined e.g. by anappropriate inclination sensor of the third sensor unit 42. Thus, usingthe relation represented by the reference plane in FIG. 8 , which may bestored either as a formula or as a look-up table, the drive controller33 calculates a maximum acceleration value. Further, the drivecontroller 33 determines a desired vehicle acceleration based on thepedaling performance of the user. For instance, the total powergeneration by the generator 13 may be monitored and if this powergeneration is above a certain predefined value, this is interpreted as adesire of the user to accelerate, e.g. at 0.7 m/s². However, if thedetermined maximum acceleration value is below the desired vehicleacceleration, the drive controller 33 controls the electric motor 21 sothat the maximum acceleration value is not exceeded.

It should be noted that the maximum acceleration value is actuallynegative for any vehicle speed and vehicle track slope beyond the boldline of FIG. 8 . In other words, the bold line also designates a maximumvelocity for the respective vehicle track slope in that the user cannotactively accelerate beyond the respective velocity. While the currentvehicle speed and the current vehicle track slope are two vehicle stateparameters on which the maximum acceleration value depends, it may alsodepend additionally or alternatively on other vehicle state parameters.For instance, it may depend on the current vehicle position, which canbe determined e.g. by a GPS sensor as part of the third sensor unit 42,and a local or national speed limit connected to the vehicle position.I.e., the drive controller 33 can look up the speed limit in acorresponding database and determine the reference plane based on thisspeed limit. Also, as an alternative to the above-mentioned inclinationsensor, the vehicle track slope may be determined by determining thecurrent vehicle position by GPS and by looking up the vehicle trackslope in a map or other corresponding database.

As mentioned above, energy for the second power electronics 22 of theelectric motor 21 may either be transferred directly from the firstpower electronics 14 of the generator 13 or from the energy storagedevice 50. There are many options how power generation can be allocatedto the user and the energy storage device 50. FIG. 9 is a diagramillustrating one such option, with the abscissa being the batterycurrent from the energy storage device 50 and the ordinate being thepercentage of the power generation allocated to the user, i.e., thegenerator 13. The percentage changes gradually as a function of thecurrent from the energy storage device 50. Of course, the percentagealso changes as a function of the electrical power provided by theenergy storage device 50 (which is proportional to the voltage timescurrent). It is almost constant at 40% within a certain range where thebattery current is between 0 and 3 times the nominal current. As thebattery current increases above 3 times the nominal current, thepercentage also increases, e.g. according to a polynomial function, andrises significantly when the current exceeds 4 times the nominalcurrent. At 5 times the nominal current, 100% of the power generation isallocated to the generator 13. However, it should be noted that althoughthe increase in the percentage is considerable, it is still gradual,i.e. there are no “jumps”. Therefore, the user may feel and increasingstrain, which, however does not increase abruptly but steadily. However,as the battery current becomes negative, i.e. energy is recuperated, thepercentage is decreased steadily, e.g. according to a polynomialfunction. Such a vehicle behavior protects the battery from beingoverstrained.

FIG. 10 shows a schematic representation of components of an electricvehicle 101 according to another embodiment. The electric vehicle 101according to the present embodiment corresponds to the electric vehicle100, discussed in the preceding with reference to FIG. 1 , with theexception that the control unit 30 further comprises a user trajectorymodeler 34 and a trajectory library 35. The trajectory library 35comprises a plurality of reference trajectories, including user-definedreference trajectories that are generated by the user trajectory modeler34.

The user trajectory modeler 34 is configured to store a user-definedreference trajectory into trajectory library 35 using machine learning,such as deep learning. In the present embodiment, while a defined useris riding the vehicle 101, the user trajectory modeler 34 analyzes thepedaling-torque-time-history of this specific user in order to derive atleast a reference trajectory that is user-specific. The user-definedreference trajectory is then stored in trajectory library 35 and can beretrieved from the trajectory library 35 during the next ride.

For example, the user trajectory modeler 34 may analyze the waveform bydetermining average value, amplitude in relation to the average, Fouriercoefficients, without limitation. Based on the waveform analysis, it isdetermined if the waveform is sinusoidal, more triangular, or comprisesany asymmetry, to derive the user-defined reference trajectory. In someembodiments, the time sequence of the pedaling movements is analyzed todetermine repeating patterns or irregularities and differences betweenleft and right leg.

The current embodiment allows to choose a more optimal referencetrajectory upon start of pedaling, and during some consecutive pedalrevolutions, until the control unit 30 had time to analyze thetorque-time history of the current operation in detail and to then adaptthe reference trajectory, as discussed in the preceding with referenceto FIG. 3 .

The operation of control unit 30 of FIG. 10 is shown in the flow diagramof FIG. 11 . The operation corresponds to the operation, discussed inthe preceding with reference to FIG. 3 with the following exceptions.

In step 301 a, the initial parameters comprise an identification of theuser, e.g., using a smartphone-vehicle or RFID-card-vehiclecommunication, entry of a user ID or PIN, or any other suitable methodof identification.

On the basis of the user identification, a user-defined referencetrajectory of the user is retrieved from the trajectory database 35 instep 302 a. The operation then continues with step 303, as discussed inthe preceding. Thus, the user-defined reference trajectory serves inparticular as “startup guidance”.

In case the current user is new to vehicle 101, i.e., no user-definedreference trajectory is present for this user in trajectory library 35,the operation proceeds from step 301 b to step 302 as discussed withreference to FIG. 3 . Accordingly, a standardized reference trajectoryis then used. Steps 303-308 correspond to the operation, discussed withreference to FIG. 3 .

In step 308 and as discussed in the preceding with reference to FIG. 3 ,the reference trajectory is adapted. As discussed with reference to FIG.3 , the adapted reference trajectory is used in following step 303 toguide the pedal along the new reference trajectory.

As follows from FIG. 11 , in step 309, the adapted reference trajectoryand/or the measured input torque in parallel is provided to the usertrajectory modeler 34.

Based on the received data in step 309, the user trajectory modeler 34in step 310 generates (i.e., if there is no previously storeduser-defined reference trajectory for this user) or updates (i.e., ifthere is a previously stored user-defined reference trajectory for thisuser) a user-defined reference trajectory, stored in library 35. As willbe apparent, the user-defined reference trajectory is improved withevery iteration of the loop of steps 303-309 and will match the currentuser more closely.

The user trajectory modeler 34 may for example use a “Waveform Transfer”to update the user-defined reference trajectory, using a method from thefield of human-machine-interaction, such as imitation and blending,without limitation.

Waveform transfer can be conducted by separating the smoothed periodicalcontent of the current user's reference trajectory from the time averageof the torque and superposing, eventually after scaling of thatperiodical content onto the time average of a previous user-definedreference trajectory or, in case no such previous user-defined referencetrajectory exists, onto a standardized reference trajectory.

Alternatively, Fast Fourier Transform and digital filtering may be usedto extract the main elements of the waveform, which are then applied toa reference trajectory (user-defined or standardized), or stored in thelibrary 35 correspondingly.

In some embodiments, a plurality of user-defined reference trajectoriesfor each user are stored in library 35. The plurality of theseuser-defined trajectories are stored as “context-depending”trajectories, i.e., each trajectory comprises trip-metadata, for exampleregarding slope, headwind or weight of the vehicle 101, including theweight of any towed trailer. Accordingly, in step 302 a, an associatedor “closest match” user-defined reference trajectory is loaded from theplurality user-defined reference trajectories for the current user,depending on the current trip-metadata. For example, in case it isdesired to use the vehicle 101 on a mountainous course (as provided tothe vehicle 101 by the user in step 301 a), a corresponding mountainoususer-defined reference trajectory is selected, i.e., a referencetrajectory, stored during the user's last ride in mountainous terrain.

Machine learning may not only be applied to the torque-time-historiesand corresponding reference trajectories of one single person or user,but to a group of riders. This way, the reference trajectory library 35“learns” and thus contains statistical information about groups ofcyclists.

The correspondingly determined user-defined reference trajectory may notonly be used by the haptic renderer 31, but also by drive controller 33.In particular, knowledge about the cycling behavior of the user may beused to recognize pedaling torque peaks more specifically and precisely.

Pedaling torque peak recognition allows for a more efficient control ofthe electric motor 21. No periodical content in the motor drive torqueimproves traction on slippery ground. This also leads to a moreefficient use of the energy used to drive the vehicle, to decreasebattery discharge, while a spontaneous pedal peak impulse by the usermay lead to a drive torque peak by the electric motor 21. That meansthat spontaneous and intuitive actions by a user are reflected in howthe vehicle moves, leading to ergonomic compatibility.

In some embodiments, the drive controller 33 comprises a digital filter(not shown), which is configured to distinguish between the periodic andthe stochastic components in the input torque, applied by the user tothe pedals 11 during operation, and to filter out the periodicalcomponents.

Stochastic signal components, i.e., pedal torque impulses or peaks inthe torque applied to the pedals 11 can be distinguished from regular,statistically common pedal torque input thanks to the fact that learntpatterns of applying torque to the pedals and the statistics of suchpatterns are known based on learning. Real time signal analysis methodsfrom the field of digital signal processing for online analysis of timeseries are applied.

Once peaks in the input torque course are recognized, these peaks andthe periodic pedaling are mathematically separated.

From the training data, received by the user trajectory modeler 34,about pedal torque and pedal torque in dependence of pedal position, itis known which torque levels at a certain pedal position are typical forregular pedaling, and which levels are typical for pedal torqueimpulses. This knowledge is used for separating periodical signalcontent from pedal torque impulses. The present embodiment allows todrive the electric motor 21 with a drive signal that does not comprisesignificant periodic signal content stemming from bipedal pedaling.

However, the motor 21 may transmit the full or attenuated peaks in thetorque course measured at the pedals 11 also to the wheels, leading toan instantaneous acceleration of the vehicle during the duration of sucha pedal torque impulse. This assures that pedaling with high intensityleads to a response by the vehicle 101 that corresponds to theexpectations of the user, and thus, ergonomic compatibility is assured.

In one embodiment, e.g., for the real time analysis of the pedal torquecourse to determine pedaling patterns, it is possible to rely ontraining data of, e.g., the last three seconds. Additionally oralternatively, information about pedaling torque patterns learnt duringprevious rides, e.g., hours or even days ago, is analyzed to morereliably recognize pedal torque impulses.

In some embodiments, the digital filter can be parameterized to notattenuate peaks or to attenuate only to a certain degree, and to less ormore attenuate or even totally block periodical pedaling (apart from themean torque) differently from patterns recognized as peaks. Since thetransmission of torque and hence pedal and vehicle speed happens more orless attenuated from pedals 11 to the driven wheel 23, theparameterization allows to customize vehicle behavior.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Combinations ofmultiple embodiments are certainly possible and within the scope of thepresent invention.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. For example, it is possible to operate the invention inan embodiment in which:

-   -   rather than using the dynamical equation (Eq. 1), the inertia        modeler 31 uses a power balances model to derive reference        trajectories from the torque-time-history of the user, namely by        determining work increments by pedaling (work        increment=momentaneous torque*pedal position angle increment).        Work increments add to the kinetic energy of the vehicle. During        the time needed for the pedals 11 to travel through the pedal        position angle increment, however, drag consumes some kinetic        energy—drag slows down the vehicle, consumes kinetic energy,        unless drag is compensated by enough work. On slopes, kinetic        energy is also transformed into potential energy (or vice versa        on downslopes). The vehicle speed is then easily derived from        kinetic energy, and by dividing through the virtual gear ratio,        pedal speed may be calculated. Consecutive values for pedal        speed allow to mathematically construct the reference trajectory        on behalf of the haptic renderer;    -   rather than using the dynamical equation (Eq. 1), the inertia        modeler 31 uses (ultra)fast convolution hardware. In this        embodiment, an impulse response function (IRF) is convolved        using the torque-time-history of the user. The impulse response        function IRF of a cycle resp. of a pedal of a cycle describes,        how the cycle resp. the pedal reacts to one single push onto the        pedal. Convolution repeated at high frequency of such an impulse        response function with the torque-time-history yields an adapted        reference trajectory; and/or    -   in particular for vehicles used in logistics or in sharing        schemes, remote diagnosis of the electrical system including but        not limited to the control unit 30, components like        generator-motor controllers, motor-generator controllers,        windings of electrical machines, intermediate circuits (DC        intermediate circuit), main switch, and battery, is provided to        determine the availability of individual or fleet vehicles        anytime in between, before, or during use. In vehicles        representing such an embodiment, there is e.g. a serial bus        connected to the components mentioned above and to e.g. a mobile        phone gateway in order that remote diagnosis is possible. During        such a diagnosis the battery may be switched on so that voltage        and current for measurements in e.g. the windings of the        electrical machines are available.

After the diagnosis, the battery is switched off again or goes into asleep mode using only very little of the battery's capacity over time.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. A single processor, module or other unit may fulfill thefunctions of several items recited in the claims, or the functionsallocated to one element may also be allocated to several distributedelements.

The mere fact that certain measures are recited in mutually differentdependent claims does not indicate that a combination of these measuredcannot be used to advantage. A computer program may bestored/distributed on a suitable medium, such as an optical storagemedium or a solid-state medium supplied together with or as part ofother hardware, but may also be distributed in other forms, such as viathe Internet or other wired or wireless telecommunication systems. Anyreference signs in the claims should not be construed as limiting thescope.

What is claimed is:
 1. A pedal drive system for generating electricalpower from muscle power of a user with at least one pedal; an electricgenerator connected mechanically with said at least one pedal; and acontrol unit for controlling a feedback torque applied at said pedal;wherein the control unit comprises a trajectory database, comprising atleast one user-defined pedal reference trajectory, and a hapticrenderer, configured for control of said feedback torque based on the atleast one user-defined pedal reference trajectory; wherein the at leastone user-defined pedal reference trajectory is based on pedalingbehavior of the user during prior use of the pedal drive system.
 2. Thepedal drive system according to claim 1, further comprising a usertrajectory modeler, configured to receive a torque course during use andto generate or update the at least one user-defined pedal referencetrajectory based on the torque course.
 3. The pedal drive systemaccording to claim 1, wherein the control unit further comprises aninertia modeler, configured to iteratively adapt the at least oneuser-defined pedal reference trajectory to obtain at least one adapteduser-defined pedal reference trajectory, wherein the at least oneadapted user-defined pedal reference trajectory is provided to thehaptic renderer for control of said feedback torque.
 4. The pedal drivesystem according to claim 3, further comprising a user trajectorymodeler, configured to receive the adapted pedal reference trajectoryand to generate or update the at least one user-defined pedal referencetrajectory based on a received past torque course.
 5. The pedal drivesystem according to claim 1, wherein the at least one user-defined pedalreference trajectory corresponds to a pedal cadence referencetrajectory.
 6. The pedal drive system according to claim 1, wherein thehaptic renderer is configured for impedance control of said feedbacktorque so that movement of the pedal is adapted to the at least oneuser-defined pedal reference trajectory.
 7. The pedal drive systemaccording to claim 3, wherein the inertia modeler is configured to adaptthe at least one user-defined reference trajectory based on at least onetrajectory parameter.
 8. The pedal drive system according to claim 3,wherein the inertia modeler is configured to: determine a past torquecourse for a predefined sampling time, determine a reference torquecourse, corresponding to the at least one user-defined referencetrajectory, for said predefined sampling time using a vehicle model,conduct a comparison of the past torque course with the reference torquecourse, and to determine at least one adapted user-defined pedalreference trajectory based on said comparison.
 9. The pedal drive systemaccording to claim 1, wherein the control unit comprises multipledifferent pedal reference trajectories.
 10. The pedal drive systemaccording to claim 1, wherein said haptic renderer is configured toselect one of said multiple reference trajectories automatically basedon a trajectory selection signal.
 11. The pedal drive system accordingto claim 3, wherein said inertia modeler is configured to iterativelyadapt the at least one user-defined pedal reference trajectory atpredetermined intervals which correspond to less than one revolution ofsaid pedal, in particular at most 10 degrees, at most 5 degrees or atmost 3 degrees of rotation angle of said pedal.
 12. An electric vehiclewith a pedal drive system according claim 1, comprising an electronictransmission connecting said generator to an electric load, and/or anelectric drive motor.
 13. A training apparatus with a pedal drive systemfor generating electrical power from muscle power of a user with atleast one pedal; an electric generator; connected mechanically with saidat least one pedal; and a control unit for controlling a feedbacktorque; applied at said pedal; wherein the control unit comprises atrajectory database, comprising at least one user-defined pedalreference trajectory, and a haptic renderer, configured for control ofsaid feedback torque based on the at least one user-defined pedalreference trajectory.
 14. A method of operating a pedal drive system forgenerating electrical power from muscle power of a user with at leastone pedal and an electric generator, connected mechanically with said atleast one pedal, comprising: controlling a feedback torque, applied atsaid pedal, based on at least one user-defined pedal referencetrajectory; wherein the at least one user-defined pedal referencetrajectory is based on pedaling behavior of the user during prior use ofthe pedal drive system.
 15. A pedal drive system for generatingelectrical power from muscle power of a user with at least one pedal; anelectric generator connected mechanically with said at least one pedal;and a control unit for controlling a feedback torque applied at saidpedal; wherein the control unit comprises a trajectory database,comprising at least one user-defined pedal reference trajectory, and ahaptic renderer, configured for control of said feedback torque based onthe at least one user-defined pedal reference trajectory; wherein thecontrol unit further comprises an inertia modeler, configured toiteratively adapt the at least one user-defined pedal referencetrajectory to obtain at least one adapted user-defined pedal referencetrajectory, wherein the at least one adapted user-defined pedalreference trajectory is provided to the haptic renderer for control ofsaid feedback torque.
 16. The pedal drive system according to claim 15,further comprising a user trajectory modeler, configured to receive theadapted pedal reference trajectory and to generate or update the atleast one user-defined pedal reference trajectory based on a receivedpast torque course.
 17. The pedal drive system according to claim 15,wherein the inertia modeler is configured to adapt the at least oneuser-defined reference trajectory based on at least one trajectoryparameter.
 18. The pedal drive system according to claim 15, wherein theinertia modeler is configured to: determine a past torque course for apredefined sampling time, determine a reference torque course,corresponding to the at least one user-defined reference trajectory, forsaid predefined sampling time using a vehicle model, conduct acomparison of the past torque course with the reference torque course,and to determine at least one adapted user-defined pedal referencetrajectory based on said comparison.
 19. The pedal drive systemaccording to claim 15, wherein said inertia modeler is configured toiteratively adapt the at least one user-defined pedal referencetrajectory at predetermined intervals which correspond to less than onerevolution of said pedal, in particular at most 10 degrees, at most 5degrees or at most 3 degrees of rotation angle of said pedal.
 20. Anelectric vehicle with a pedal drive system according claim 15,comprising an electronic transmission connecting said generator to anelectric load, and/or an electric drive motor.
 21. A method of operatinga pedal drive system for generating electrical power from muscle powerof a user with at least one pedal and an electric generator, connectedmechanically with said at least one pedal, comprising: controlling afeedback torque, applied at said pedal, based on at least oneuser-defined pedal reference trajectory; and iteratively adapting the atleast one user-defined pedal reference trajectory to obtain at least oneadapted user-defined pedal reference trajectory.